Recent well logging techniques have become very sophisticated. Ultrasonic detection and nuclear magnetic imaging are now commonplace. Despite the many advances in detection methods, the interpretations of the results are often cumbersome, laborious, or somewhat inaccurate.
One of the more time consuming evaluations involves the interpretation of reflection amplitude images obtained by an Ultrasonic Borehole Imaging (UBI) tool, or electrical conductivity images obtained by a Fullbore Formation MicroImaging (FMI) tool. For a detailed description of UBI and FMI tools and techniques, see: Hayman, A. J., Phillipe Parent, Philip Cheung, and Patrick Verges, "Improved Borehole Imaging by Ultrasonics," Soc. of Petr. Eng., SPE 28440, pp. 977-992 (25-28 Sep. 1994); and Safinya, K. A., P. Le Lan, M. Villegas, and P. S. Cheung, "Improved Formation Imaging with Extended Microelectrical Arrays," Soc. of Petr. Eng., SPE 22726, pp. 653-664 (6-9 Oct. 1991), respectively. One of the problems with these detection methods is the difficulty in rapidly and easily characterizing fractures, formation dips, and other events in reservoir regions.
Extraction of dips and azimuths of fractures and formation beddings in the workstation environment is a tedious effort. A planar dipping event (e.g., a planar fracture, or a planar bed boundary) can be represented on borehole images as a sinusoid with one period, when unrolled and displayed on the workstation.
A typical borehole image containing such sinusoids is completely specified by its amplitude and phase, which are functions of dip angle and azimuth of the planar event. Often, the geologist must fit best sinusoids on the borehole images interactively. This process is labor intensive. One present day method of doing this is to choose several points along these sinusoidal features, and then fit the best sinusoids based on the chosen points. Another current procedure is to modify amplitudes and phase of sinusoids interactively on the workstation until a satisfactory fit is obtained.
It would be desirable to have a method of instantaneously or quickly interpreting this information.
The present invention reflects the discovery of a procedure for rapidly extracting dips and azimuths of fractures and formation beddings from the image data.
The technique of this invention significantly reduces the interpretation time for production geologists by automatically extracting these features or geometric parameters from borehole images. The inventive technique utilizes a Hough transform, as described in U.S. Pat. No. 3,069,654, issued Dec. 18, 1962 to P. V. C. Hough, for METHOD AND MEANS FOR RECOGNIZING COMPLEX PATTERNS; J. Illingworth and J. Kittler, "A Survey of the Hough Transform", Comput. Vision, Graphics, Image Process. 44 (1988), 87-116; and V. F. Leavers, "Which Hough Transform?", CVGIP: Image Understanding 58 (1993), no. 2, 250-264.
The Hough transform technique of this invention is robust to noise or gaps in the images. It can subsequently detect and characterize other geometric features (e.g., linear, circular, or ellipsoidal shapes). Some of these shapes may represent vugs in carbonate reservoirs present in the images.
In U.S. Pat. No. 5,162,994, issued to Torres on Nov. 10, 1992, for METHOD FOR DETERMINING DIP AND STRIKE ANGLES IN BOREHOLE ULTRASONIC SCANNING TOOL DATA, a method is illustrated for interpreting borehole data using Hough transforms. This patented method uses images obtained by the BoreHole TeleViewer (BHTV) or a Circumferential Acoustic Scanning Tool (CAST).
The present invention is significantly different from the method used in the aforementioned patent, and provides a much wider scope of improvement. The current invention improves the prior Hough transform method by:
a) using the edge slope/orientation information for further constraining the Hough transform; PA1 b) iteratively using Hough transforms for detecting not only sinusoids, but also different geometric objects such as lines, circles, and ellipses; and PA1 c) smoothing the data to improve the accuracy of the Hough transform.